1. Field of the Invention
The present invention generally relates to fingerprint sensor packages, more specifically, a package wherein an LSI (Large Scale Integrated circuit) chip for reading a fingerprint is exposed on a surface thereof.
2. Description of the Related Art
Recently and continuing, for improvement of security, a fingerprint identification apparatus is provided at an electronic device such as a personal computer or a cellular phone. It is necessary for the fingerprint identification apparatus to read the fingerprint and therefore a fingerprint sensor package for reading the fingerprint is provided at the fingerprint identification apparatus. It is required for the fingerprint identification apparatus to securely identify the fingerprint in order to improve the security and therefore it is desired to improve the precision of the identification of the fingerprint.
An LSI chip (fingerprint sensor) for reading a pattern of the fingerprint is installed in the fingerprint sensor package. Generally, a capacitance sensor, a pressure sensor, or the like, is used as the fingerprint sensor. As the fingerprint sensor package, there are an area-type finger print sensor and a sweep-type finger print sensor. In the area-type finger print sensor, the fingerprint is read by positioning a finger on a fingerprint sensor having a plane configuration. In the sweep-type finger print sensor, the fingerprint is read by moving the finger on a liner-state finger sensor. Fingerprint data read by the finger sensor are sent to a fingerprint data process apparatus provided at an outside of the fingerprint sensor package. The fingerprint data are image-processed by the fingerprint data process apparatus so that the fingerprint is extracted.
Generally, the above-mentioned fingerprint sensor package includes an LSI chip (fingerprint sensor), a substrate, molded resin, an external connection terminal, and others. The LSI chip is used for detecting the fingerprint and is fixed to the substrate. See page 5 and FIG. 3 of Japan Laid-Open Patent Application 2003-235830.
The substrate is, for example, a resin substrate. Designated wiring patterns are formed on upper and lower surfaces. The wiring patterns formed on the upper and lower surfaces of the substrate are electrically connected to each other via a via-hole forming part which pierces the substrate. The LSI chip is provided on the upper surface of the substrate. The external connection terminal is provided at the lower surface of the substrate. The LSI chip and the wiring pattern formed on the upper surface of the substrate are electrically connected by a gold wire. A solder ball functioning as the external connection terminal is connected to the wiring pattern. Furthermore, molded resin is formed at an external circumference position of the LSI chip other than an area where the finger touches, in order to protect the gold wire or the like.
In the above-mentioned conventional fingerprint sensor package, both the LSI chip and the substrate have plane configurations. In addition, since the LSI chip is fixed to the substrate having a plane plate configuration and good mechanical strength, the LSI chip does not flexibly deform even in a case where the LSI chip is pushed by the finger.
However, since the LSI chip for detecting the fingerprint has a plane configuration which does not correspond to the configuration of the finger (namely curved configuration), there is a problem in that precision of reading the fingerprint is degraded. That is, in a case where the LSI chip has a plane configuration, if the finger is put on the LSI chip, a center position of the finger comes in contact with the LSI chip but a gap between the finger and the LSI chip is generated at both sides of the finger. That is, at both sides of the finger, the finger is separated from the LSI chip so that the fingerprint data sufficient for fingerprint identification cannot be generated by the LSI chip.
In order to solve the above-mentioned problem, there is a method in which a fingerprint reading process is implemented by strongly pushing the finger to the LSI chip. However, in this method, the workload of the person who implements the fingerprint identification increases so that operability may be degraded. Furthermore, since there are differences among individuals as for the force to push, the LSI may be pushed too strongly. Therefore, it is necessary to improve the strength of the LSI chip. However, in order to improve the strength of the LSI chip, for example, it is necessary to make the thickness of the substrate greater or increase the amount of the molded resin to be provided. This causes an increase of cost and size of the fingerprint sensor package.